The present invention relates generally to membrane switches and, more particularly, to a multiple layer membrane switch having at least two surfaces having contact members thereon.
Known membrane switches comprise two or more layers of flexible plastic. Such switches are normally employed in the touch control panels or keyboards of devices such as microwave ovens and computers. Normally a top layer of flexible plastic is provided having indicia thereon to identify the particular function of each switch area. A second layer is provided adjacent the top layer and includes contact members in registration with the particular indicia. In registration means that the particular indicia and its corresponding contact member are in two dimensional alignment. Pushing on or compression of the flexible layer at or near the indicia causes a flexing or movement of the second layer at or near the contact member. Usually a spacer layer is provided adjacent the second layer, with the spacer layer having apertures in registration with the contact members of the second layer. Such spacer layer usually comprises a type of foam membrane such as disclosed in U.S. Pat. No. 4,345,119. A fourth layer is provided adjacent the spacer layer. Such fourth layer usually comprises the grounded metal chassis of the particular device in which the membrane switch is being utilized. Upon the compression of the flexible indicia and resulting movement of the contact member of the second layer, contact is made between the contact member and the ground layer, thereby completing the particular switch circuit associated with the contact. The contact members of the second layer are connected to a series of leads extending from the switch assembly.
Another membrane switch arrangement that is known comprises an indicia bearing top layer of a flexible plastic material. A second layer of flexible plastic is provided adjacent the top layer. The second layer contains contact members in registration with particular indicia of the top layer. A spacer layer is provided adjacent the second layer and having apertures in registration with the contact members of the second layer. A fourth non-conductive layer is provided having contact members in registration with certain of the second layer contact members. Upon the compression of an indicia bearing area of the top layer, the contact member of the second layer in registration therewith is flexed so as to make connection between the contact area of the second layer and the contact area of the fourth layer in registration therewith. Each of the second layer contact members and the fourth layer contact members are connected to a series of leads which extend from the switch assembly.
The main limitation of the above described arrangements are that they provide for a single circuit connection. In the arrangement wherein the contact members are shorted against the ground layer, a single layer of external leads extends from the contact member layer. Even in the arrangement where two sets of leads extend from the two layers of contact members, only a single layer of connections is formed upon the connection of the contact members of the one layer with the contact members of the second layer. The connection possibilities are limited to the connection of a contact member on the one layer to a contact member on the ground or other layer.
In changing the graphics or design of a control panel, it is extremely difficult to change the switch arrangement adjacent such graphics without changing the printed circuit board to which the switch leads are attached. The reason for such difficulty is that the repositioning or addition of graphics requires the repositioning of contact members so that the leads may extend to the same positions on the circuit board, as it is desirable to utilize the same proven design of circuit board to control the various functions of the device to which it is connected. The connection of the leads to the same positions of the circuit board, without utilizing undesirable cross-overs, becomes an extremely difficult task when only one layer of switches is available for contact with the newly arranged indicia. Even when two separate layers include contact members, the switch connection possibilities are limited to the connection of contact members on one layer to contact members on the other layer.
Accordingly, it is an object of the present invention to provide an improved membrane switch assembly by utilizing multiple contact bearing surfaces.